Preheat oven to 180°C/350°F. Butter a 42x30cm (17x12in) rimmed baking sheet, line with foil and butter the foil as well.
Whisk together flour, baking soda, salt, and spices.
Beat butter and brown and granulated sugars with a mixer on medium-high speed until pale and fluffy. Add eggs and yolk, 1 at a time, beating well after each addition and scraping down sides of bowl as needed. Beat in vanilla and molasses. Reduce speed to low. Gradually add flour mixture, and beat until just combined. Stir in white chocolate.
Spread batter into prepared pan. Bake until edges are golden, about 25 minutes*. Let cool completely in pan on a wire rack. Cut into 5cm (2in) squares or desired shape.
The blondies can be stored in an airtight container for up to 1 week.

* I needed to bake mine for 35 minutes, the mixture puffed while in the oven then flattened in the center after cooling

Hi, Patricia. I'm Spanish and in Spain it's not usual at all to find recipes which include this kind of spices, but I must confess that I love them, as you do. So I'll have a look at Martha's recipes collection to get ideas.